Application selection of memory request scheduling

ABSTRACT

The present disclosure generally describes systems, methods and devices for operating a computer system with memory based scheduling. The computer system may include one or more of an application program and a memory controller in communication with memory banks. The memory controller may include a scheduler for scheduling requests. The application program may select a scheduling algorithm for scheduling requests from a plurality of scheduling algorithms. The application program may instruct the scheduler to schedule requests using the selected scheduling algorithm.

REFERENCE To RELATED APPLICATIONS

This application is related to the following applications, application Ser. No. 12/507,696 entitled “Batch Scheduling With Segregation” filed Jul. 22, 2009, now issued U.S. Pat. No. 8,607,234 and application Ser. No. 12/508,457 entitled “Scheduling Of Threads By Batch Scheduling” filed Jul 23, 2009, currently pending.

BACKGROUND

In a chip-multiprocessor (CMP) system, the DRAM system is shared among cores. In a shared DRAM system, requests from a thread can not only delay requests from other threads by causing bank conflicts, bus conflicts or row-buffer conflicts, but they can also destroy DRAM-bank-level parallelism of other threads. Requests with latencies that would otherwise have been overlapped could effectively become serialized. As a result, both fairness and system throughput may degrade, and some threads can starve for long time periods.

One approach to providing fair and high-performance memory scheduling is using a scheduling algorithm called parallelism-aware batch scheduling (PAR-BS), as shown in Onur Mutlu and Thomas Moscibroda, “Parallelism-Aware Batch Scheduling: Enhancing both Performance and Fairness of Shared DRAM Systems,” isca, pp. 63-74, 2008 (2008 International Symposium on Computer Architecture), all of which is incorporated by reference herein, except where inconsistent with the present application. PAR-BS design is based on two ideas: (1) request batching; and (2) parallelism-aware memory scheduling. First, PAR-BS processes DRAM requests in batches to provide fairness and to avoid starvation of requests. Second, to optimize system throughput, PAR-BS employs a parallelism-aware DRAM scheduling policy that aims to process requests from a thread in parallel in the DRAM banks, thereby reducing the memory-related stall-time experienced by the thread. PAR-BS incorporates support for system-level thread priorities and can provide different service levels, including purely opportunistic service, to threads with different priorities.

BRIEF DESCRIPTION OF THE DRAWINGS

Subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings:

FIG. 1 illustrates a computer system;

FIG. 2 illustrates an application program being executed by an operating system;

FIG. 3 illustrates a schematic representation of an application program being divided into threads which issue requests sent to a memory controller, including a detailed view of a scheduler of a memory controller in FIG. 3A;

FIG. 4 depicts a flowchart illustration of methods, apparatus (systems) and computer program products for Batch Scheduling with Segregation;

FIG. 5 depicts a schematic representation of requests from threads being arranged in batches for Batch Scheduling with Segregation; and

FIG. 6. depicts a flowchart illustration of methods, apparatus (systems) and computer program products; all arranged in accordance with at least some embodiments of the present disclosure

DETAILED DESCRIPTION

The following description sets forth various examples along with specific details to provide a thorough understanding of claimed subject matter. It will be understood by those skilled in the art, however, that claimed subject matter may be practiced without some or more of the specific details disclosed herein. Further, in some circumstances, well-known methods, procedures, systems, components and/or circuits have not been described in detail in order to avoid unnecessarily obscuring claimed subject matter. In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

In the following description, algorithms and/or symbolic representations of operations on data bits and/or binary digital signals stored within a computing system, such as within a computer and/or computing system memory may be presented. An algorithm is generally considered to be a self-consistent sequence of operations and/or similar processing leading to a desired result where the operations may involve physical manipulations of physical quantities that may take the form of electrical, magnetic and/or electromagnetic signals capable of being stored, transferred, combined, compared and/or otherwise manipulated. In various contexts such signals may be referred to as bits, data, values, elements, symbols, characters, terms, numbers, numerals, etc. Those skilled in the art will recognize, however, that such terms may be used to connote physical quantities. Hence, when terms such as “storing”, “processing”, “retrieving”, “calculating”, “determining” etc. are used in this description they may refer to the actions of a computing platform, such as a computer or a similar electronic computing device such as a cellular telephone, that manipulates and/or transforms data represented as physical quantities including electronic and/or magnetic quantities within the computing platform's processors, memories, registers, etc.

The disclosure is drawn, inter alia, to methods, apparatus, systems and computer program products related to application selection of memory request scheduling. The present disclosure also generally makes use of the discovery of using an application program to select a scheduling algorithm for scheduling requests, from a plurality of scheduling algorithms, and instructing a memory controller to use the selected scheduling algorithm.

FIG. 1 illustrates a computer system arranged according to at least some embodiments of the present disclosure. FIG. 1 illustrates a computer 100 including a processor 110, memory 120 and one or more drives 130. The drives 130 and their associated computer storage media may provide storage of computer readable instructions, data structures, program modules and other data for the computer 100. Drives 130 may include an operating system 140, application programs 150, program modules 160, and database 180. Operating system 140 and/or application programs 150, for example, may include program instructions for causing the computer 100 to carry out the functions and/or operations specified in FIG. 6, for example, scheduling algorithm 153, which is a part of an application. Computer 100 may include user input devices 190 through which a user may enter commands and data. Input devices may include an electronic digitizer, a microphone, a keyboard and pointing device, commonly referred to as a mouse, trackball or touch pad. Other input devices may include a joystick, game pad, satellite dish, scanner, or the like.

These and other input devices may be coupled to processor 110 through a user input interface that may be coupled to a system bus or it may be connected by other interface or bus structures, such as a parallel port, game port or a universal serial bus (USB), or the like. Computer 100 may include peripheral output devices such as speakers, a printer, or a display 202, which may be connected through an output peripheral interface 194 or the like.

Computer 100 may be configured to operate in a networking environment using logical connections to one or more computers, such as a remote computer connected to network interface 196 The remote computer may be a personal computer (PC), a server, a router, a network PC, a peer device or other common network node, and may include many or all of the elements described above relative to computer 100.

Networking environments may include offices, enterprise-wide area networks (WAN), local area networks (LAN), intranets and the Internet. In an example, computer 100 may be the source machine from which data is being migrated and the remote computer may comprise the destination machine, or vice versa. Source and destination machines may not be connected by a network 108 or any other means, but instead, data may be migrated via any media capable of being written by the source platform and read by the destination platform or platforms. In a LAN or WLAN networking environment, computer 100 may be connected to the LAN or WAN through a network interface 196 or an adapter. In a WAN networking environment, computer 100 may include a modem or other means for establishing communications over the WAN, such as the Internet or network 108. Other means of establishing a communications link between the computers may be used.

A computer peripheral may include any device coupled to the processor 110 and the memory 120 of the computer 100 through the system bus. A computer peripheral may include any device connected with the output peripheral interface, including the display 202, the printer, or speakers, drives 130, user input devices 190 such as the keyboard, the mouse, and the microphone, and the network interface 196. Components of the computer peripheral may include any device within a computer peripherals which may use power and may be any device, such as speakers, lighting elements such as light emitting diodes, or backlights used to provide lighting for displays, display elements, such as LCD, LED, OLED, CRT, or Plasma displays, or semiconductor chips such as a central processing unit (CPU), a graphic processing unit (GPU), memory.

FIG. 2 illustrates an application program being executed by an operating system, arranged in accordance with at least some embodiments of the present disclosure. As shown in FIG. 2, operating system 140 may execute an application program 150 from drives 130. Operating system 140 and/or application programs 150, for example, may include program instructions for causing the computer 100 to carry out the functions and/or operations specified in FIG. 6. Application program 150 may be any application, program, portion of a program, or thread, which may be executed by operating system 140 in multiprocessor 111. Application program 150 may be configured to load data 230 into memory 120 and accesses data 230 from memory 120 using a memory controller 210. Application program 150 may be arranged to run multiple sub-applications called threads 220 to accomplish a task, such as loading and accessing data 230 into and from memory bank 122 of memory 120 using one or more requests 226. Threads 220 may be executed by application program 150. Application program 150 may be arranged to divide the execution of a task into as many threads 220 as application programs deems necessary to accomplish that task. For example, if application program 150 is a word processing program with a document having multiple pages, and application program 150 is configured to accomplish the task of spell checking each page of the document, application program 150 may be arranged to divide the task of spell checking the document into multiple threads 220 such that each thread 220 may spell check a portion of the document. Each thread 220 may be sent to multiprocessor 111 for execution. When executed within the multiprocessor 111, each thread 220 may produce requests 226 for data 230 within memory 120. The requests 226 may be sent to memory controller 210, which may organize the requests 226 so that multiprocessor 111 may be configured to operate efficiently.

In some embodiments, as shown in FIG. 2, multiprocessor 111 may include processors that may simultaneously execute more than one thread 220. Multiprocessor 111 may include multiple processors known as cores 412 and 512, or a single processor (only one of 412 or 512) which may run multiple threads 220 simultaneously, also known as a multithreaded processor. FIG. 2 illustrates an example multiprocessor 111 including two cores 412 and 512, but is not limited to any particular number of cores. The term “core” may be used herein to refer to any device which may process a single thread and may refer to a processor or a portion within a processor that may process a single thread. A multithreaded processor may be referred to as a processor having multiple cores. A computer 100 having multiple processors may be referred to herein as a computer 100 having multiple cores.

FIG. 3 illustrates a schematic representation of an application program being divided into threads which may issue requests sent to a memory controller in accordance with at least some embodiments of the present disclosure. As shown in FIG. 3, application 150 may be divided into multiple threads 220 _(a)-220 _(n), where n may represent the number of threads 220, and wherein each thread may perform a task for application 150 and may be executed on, for example, multiprocessor 111 of FIG. 2. The multiprocessor may be configured to receive and execute multiple threads 220 _(a)-220 _(n), individually or simultaneously, from application program 150. Each thread 220 executed on the multiprocessor may be executed independently from each other thread 220 and may issue multiple requests 226 _(a1)-226 _(no) for data 230 stored in memory 120, where the first index (a . . . n) represents the thread 220 associated with the request 226, and the second index (1 . . . o) represents the number of requests 226 associated with a particular thread 220.

Each thread 220 may issue requests 226 for data 230 stored in memory 120, and in an example, for data 230 stored in memory banks 122 _(a)-122 _(m) within memory 120, where the index (a, b . . . m) may represent the number of memory banks 122. Memory 120 may include multiple memory banks 122 _(a) to 122 _(m) that may be configured to allow multiple outstanding memory requests 226 to proceed in parallel if they seek data 230 from different memory banks. As a result, first memory bank 122 _(a) and second memory bank 122 _(b) may be accessed concurrently by memory controller 210 upon receiving a request 226 for data 230.

Each memory bank 122 may be a two-dimensional array, including columns C₁ to C_(i), where the index (1 . . . i) may represent the number of columns, and rows R₁ to R_(j), where the index (1 . . . j) may represent the number of rows. Rows may store data in consecutive memory locations and may be, for example, approximately 1-2 kilobytes (KB) in size. The data 230 in a memory bank 122 may be accessed from a row-buffer R_(B), which may contain at most one row. In an example, each memory bank 122 may contain one row-buffer R_(B). The time it takes to service each request 226 for data 230 may depend on the status of each row-buffer R_(B) and may fall into one of three categories. The first category may be row hit, where a request 226 may be to a row that may be currently open in each row-buffer R_(B), allowing the memory controller 210 to issue only a read or write command to the respective memory bank 122, resulting in a bank access latency of t_(CL).

The second category may be row closed, where there may be no open row in a row-buffer R_(B), so that the memory controller 210 may need to first issue an activate command to open a required row and then a read/write command, resulting in a total latency of t_(RCD)+t_(CL), where t_(RCD) is the latency for the activate command and t_(CL) is the latency for the read/write command. The third category may be row conflict, where a request 226 may be to a row different from the one currently in a respective row-buffer R_(B), so that the memory controller 210 needs to first issue a precharge command and open the required row (by activating it), and issue a read/write command for data in the required row. These accesses may incur the highest total latency of t_(RP)+t_(RCD)+t_(CL), where t_(RP) is the latency for the row precharge (to close it), t_(RCD) is the latency for the activate command and t_(CL) is the latency for the read/write command.

Memory controller 210 may be arranged in communication with memory 120 and the multiprocessor and may be located anywhere along the system, including within the multiprocessor. Memory controller 210 may include a memory request buffer 211 that may be arranged to buffer the requests 226 and the data 230 while the requests 226 may be waiting to be serviced. Memory controller 210 may include a scheduler 212 that may be configured to select the next request 226 to be serviced. In some embodiments, scheduler 212 may have two-levels. When selecting the next request 226 to be serviced, the scheduler 212 may be configured to consider the state of the memory banks 122 _(a)-122 _(m) and the state of memory buses 214 _(a)-214 _(m) connecting the memory controller 210 to each memory bank 122, and the state of a request 226. A memory command for a request 226 may be scheduled by the scheduler 212 if its scheduling does not cause any resource, such as memory banks 122 _(a)-122 _(m) and address/data/system bus, conflicts and does not violate any memory timing constraints. A memory command which does not cause any conflicts may be considered to be ready.

There are a variety of memory request scheduling algorithms. Examples may include (A) first-ready first-come-first-serve; (B) Network Fair Queuing, and its variation, Start-time Fair Queuing; (C) Stall-time Fair Memory Scheduler; and (D) Parallelism-aware Batch Scheduling, which uses both a batch algorithm and a within-batch scheduling algorithm, allowing for variations created by using different batch algorithms (such as Time-based Static Batching and Empty-slot Batching) and/or different within-batch scheduling algorithms (such as Parallelism-aware Within Batch Scheduling, Total-max Within Batch Scheduling, random within-batch scheduling, round-robin within-batch scheduling, and first-ready first-come-first-serve within-batch scheduling).

In addition, described in more detail below (FIGS. 4 and 5), is another memory request scheduling algorithm, (E) Batch Scheduling with Segregation, which may also use both a batch algorithm and a within-batch scheduling algorithm. In this algorithm, the batch algorithm may be adapted to group requests based on, for example, characteristics of the threads which issued the requests, such as (1) good design threads and bad design threads, based on how well the threads are designed for use with parallel memory; (2) cooperative threads and non-cooperative threads, based on how efficiently the threads work with other threads; (3) first application, second application and third application threads, based on the application program from which the thread originated; (4) large request threads, optionally medium request threads and small request threads, based on the relative number of requests the threads make, for example large request thread may make an average number of request or greater, and small request threads may make a number of requests less than an average number. Similar to Parallelism-aware Batch Scheduling, different within-batch scheduling algorithm may be used to create a number of variations (such as Parallelism-aware Within Batch Scheduling, Total-max Within Batch Scheduling, random within-batch scheduling, round-robin within-batch scheduling, and first-ready first-come-first-serve within-batch scheduling).

FIG. 3A includes a detailed view of scheduler 212 which may be used with Batch Scheduling with Segregation, showing parts of scheduling algorithm 300, including batch algorithm 302 and within-batch scheduling algorithm or parallelism-aware within-batch scheduling algorithm 350. Alternatively, both the within-batch scheduling algorithm and the parallelism-aware within-batch scheduling algorithm may be employed by the scheduling algorithm.

Referring again to FIG. 3 and FIG. 3A, in order to improve the efficiency of scheduling requests 226 _(a1)-226 _(no) from threads 220 _(a)-220 _(n), memory controller 210, and specifically scheduler 212, may be adapted to use Batch Scheduling with Segregation as a scheduling algorithm 300, which may take into account intra-thread bank-parallelism, and may provide quality of service (QoS) to each thread 220 _(a)-220 _(n). Quality of service may be considered as the ability to provide different priority to different threads 220 _(a)-220 _(n), and/or to provide a base level of performance when executing threads 220 _(a)-220 _(n). The scheduling algorithm 300 may be designed to provide a configurable substrate for fairness and QoS and high CMP system throughput. The batching algorithm 302 may be adapted to group a number of outstanding memory requests 226 _(a1)-226 _(no) into batches. The scheduling algorithm 300 may also be adapted to ensure that all requests 226 _(a1)-226 _(no) belonging to current batches are serviced before the next batches are formed. The batching algorithm 302 may be configured to form multiple batches at the same time, where each batch may be formed using certain criteria, described herein.

The batching algorithm may be arranged to group outstanding requests in the memory request buffer into sets of requests, called batches. The memory scheduler may avoid request re-ordering across batches by prioritizing requests belonging to a current batch over other requests. Once all requests of a batch are serviced, for example when the batch is finished, the next batch, which may include outstanding requests in the memory request buffer that were not included in the last batch, may then be serviced. The formation of multiple batches at the same time may allow for re-order requests within a batch.

The batching algorithm may work as follows below. Each request in the memory request buffer may have an associated bit indicating which batch the request belongs to in the current batches. If a request belongs to a first batch, for example, the associated bit may be set to indicate that the request belongs to the first batch, and the request may be considered marked. Multiple batches may be formed, where each of the requests are marked to indicate which of the multiple batches the requests are to be placed in or are a part of, based upon certain criteria, described herein. When there are no marked requests left in the memory request buffer, for example when all requests from previous batches have been completely serviced, new batches may be formed.

In some embodiments, when forming a batch, the batching algorithm may mark up to a set number, a marking-cap, of outstanding requests per memory bank for each thread; these requests may form the batch. The marking-cap may be utilized as a system parameter that may limit how many requests issued by a thread for a certain bank can be part of a batch. For instance, if the marking-cap is five and a thread has seven outstanding requests for a memory bank, the batching algorithm may mark the five oldest requests (or fewer if less than five requests exist). Examples include 2, 3, 5, 7, 10, 20, 50, or even larger marking-caps. Furthermore, for different types of batches, as described herein, the marking-caps may be different. In some examples, when no marking-cap is set, all outstanding requests may be marked when one or more batches are formed.

The batching algorithm may be arranged to prioritize marked requests (requests in batches) over non-marked requests in a given memory bank. If there are no marked requests to a given bank, outstanding non-marked requests may be scheduled to that bank. To select among two marked or two non-marked requests, any existing or new memory scheduling algorithm, such as FR-FCFS, may be employed.

FIGS. 4 and 6 are flowchart illustrations of methods, apparatus (systems) and computer program products arranged in accordance with at least some embodiments of the present disclosure. It will be understood that each block of the flowchart illustrations in FIGS. 4 and 6, and combinations of blocks in the flowchart illustration in FIGS. 4 and 6, may be implemented by computer program instructions. These computer program instructions may be loaded onto a computer, a processor, or other programmable data processing apparatus to produce a machine, such that the instructions which execute on the computer or other programmable data processing apparatus create means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a storage device that may direct a computer, a processor, or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the storage device produce an article of manufacture including instruction means which implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer, a processor, or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer, a processor, or other programmable data processing apparatus, to produce a computer implemented process such that the instructions which execute on the computer, a processor, or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.

Accordingly, blocks of the flowchart illustrations in FIGS. 4 and 6 support combinations of means for performing the specified functions/operations/actions or combinations of steps for performing the specified functions or operations and program instruction means for performing the specified functions or operations. It will also be understood that each block of the flowchart illustrations in FIGS. 4 and 6, and combinations of blocks in the flowchart illustrations in FIGS. 4 and 6 may be implemented by special purpose hardware-based computer systems which perform the specified functions/operations/actions or steps, or combinations of special purpose hardware and computer instructions.

Such computer instructions may be fixed either on a tangible medium, such as a computer readable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk) or transmittable to a computer system, via a modem or other interface device, such as a communications adapter connected to a network over a medium. The medium may be either a tangible medium (e.g., optical or analog communications lines) or a medium implemented with wireless techniques (e.g., microwave, infrared or other transmission techniques). The series of computer instructions embodies all or part of the functionality previously described herein with respect to the system.

Those skilled in the art should appreciate that such computer instructions may be written in a number of programming languages for use with many computer architectures or operating systems. Furthermore, such instructions may be stored in any memory device, such as semiconductor, magnetic, optical or other memory devices, and may be transmitted using any communications technology, such as optical, infrared, microwave, or other transmission technologies. It is expected that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (for example, shrink wrapped software), preloaded with a computer system (for example, on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the network (for example, the Internet or World Wide Web).

FIG. 4 shows an example of Batch Scheduling with Segregation. As illustrated, a method 500 for forming one or more batches of thread requests, where each of the batches may include one or more requests, may be initiated at block 501. After initiating the method 500, threads may then be segregated into (identified as) thread types, for example first thread type and second thread type, or first, second and third thread types, at block 502. One or more batches, where each of the batches may contain requests issued from the thread or threads of similar or the same thread type or types, may be formed at block 504. After forming one or more batches, where each batch may contain one or more requests, the one or more batches may then be executed by the memory controller at block 506. The one or more batches may be executed one at a time, or if the computer system is capable, they may be executed more than one at a time.

The segregation (identification) of threads, and therefore the batching of requests from the different thread types, may be based on any of a number of different criteria. For example, threads may be segregated into: (1) good design threads and bad design threads, based on how well the threads are designed for use with parallel memory; (2) cooperative threads and non-cooperative threads, based on how efficiently the threads work with other threads; (3) first application, second application and third application threads, based on the application program from which the thread originated; (4) large request threads, optionally medium request threads and small request threads, based on the relative number of requests the threads make, for example large request thread may make an average number of request or greater, and small request threads may make a number of requests less than an average number. Many other variations are possible. Accordingly, depending on the criteria selected, there may be a first thread type, a second thread type, an optional third thread type, an optional fourth thread type, etc.

FIG. 5 is an example of Batch Scheduling with Segregation, using a criteria which may result in two thread types; as noted above, more than two thread types may also be possible, depending on the criteria selected. The threads 220 _(a)-220 _(n) may be segregated into first thread type 250 and second thread type 251. Requests issued by each thread type, for example first requests 260 issued from the first thread type 250, and second requests 261 issued from the second thread type 251, may then be formed into one or more batches 232 _(a)-232 _(x) of thread requests. Each batch may include requests of one thread type, for example first batch 232 _(a) may include first requests 260, and last batch 232 _(x) may include second requests 261, as illustrated. In another example, each batch 232 _(a)-232 _(x) may contain primarily first requests 260 from the first thread type 250, or primarily second requests 261 from second thread type 261. In this manner, the batches 232 _(a)-232 _(x) formed may be homogeneous or primarily homogeneous for requests from each thread type. The one or more batch may be executed one at a time, or if the computer system is capable, they may be executed more than one at a time. The term primarily, as used herein, may be more than approximately 50%, more than approximately 80%, more than approximately 95%, or more than approximately 99%.

Once one or more batches are formed, the scheduling algorithm may arranged to employ a within-batch scheduling algorithm or a parallelism-aware within-batch scheduling algorithm, to schedule service of requests within a batch. Any within-batch scheduling algorithm may be used, such as FR-FCFS.

Within a batch, the parallelism-aware within-batch scheduling algorithm may be arranged to first prioritize row-hit requests. Second, requests from threads with higher rank may be prioritized over those from threads with lower rank. Finally, all else being equal, an older request may be prioritized over a younger request.

The parallelism-aware within-batch scheduling algorithm may be arranged to use a rank-based thread prioritization scheme within a batch. When a new batch is formed, the memory scheduler may be arranged to compute a ranking among all threads that have requests in the new batch. While the new batch is processed, the computed ranking may remain the same and requests from higher-ranked threads may be prioritized over those from lower-ranked threads.

Although any ranking-based scheme may be used, the specific ranking procedure may have a significant impact on CMP throughput and fairness. A good ranking scheme may effectively differentiate between memory-intensive and non-intensive threads (and threads with high bank-parallelism). In some implementations, a ranking scheme may be employed conforming to the shortest job first principle: it may rank the non-intensive threads higher than the intensive threads.

FIG. 6 depicts a flowchart illustration of methods, apparatus (systems) and computer program products arranged in accordance with at least some embodiments of the present disclosure. As illustrated in FIG. 6, a method 600 for memory request scheduling may be initiated at block 601. After initiating the method 600, a scheduling algorithm may be selected using an application program, at block 602. For example, the scheduling algorithm may be selected using the application program which issued the thread or threads that issued the requests. The scheduling algorithm selected may be any scheduling algorithm, such as those previously described. The application may either select the same scheduling algorithm, or may select a different scheduling algorithm based on criteria chosen during production of the application program. The scheduling algorithm selected may be a scheduling algorithm encoded in computer readable media, and may be part of an operating system, an application program, or may be provided separately. For example, the application program which issued the threads may contain one or more scheduling algorithm which may be selected using the application program. Once selected, the memory controller may then be instructed to use the selected scheduling algorithm for scheduling the requests, at block 604. The requests may then be scheduled for service, by the memory controller in accordance with the selected scheduling algorithm, at block 606.

Claimed subject matter is not limited in scope to the particular implementations described herein. For example, some implementations may be in hardware, such as employed to operate on a device or combination of devices, for example, whereas other implementations may be in software and/or firmware. Likewise, although claimed subject matter is not limited in scope in this respect, some implementations may include one or more articles, such as a storage medium or storage media. This storage media, such as CD-ROMs, computer disks, flash memory, or the like, for example, may have instructions stored thereon, that, when executed by a system, such as a computer system, computing platform, or other system, for example, may result in execution of a processor in accordance with claimed subject matter, such as one of the implementations previously described, for example. As one possibility, a computing platform may include one or more processing units or processors, one or more input/output devices, such as a display, a keyboard and/or a mouse, and one or more memories, such as static random access memory, dynamic random access memory, flash memory, and/or a hard drive.

Reference in the specification to “an implementation,” “one implementation,” “some implementations,” or “other implementations” may mean that a particular feature, structure, or characteristic described in connection with one or more implementations may be included in at least some implementations, but not necessarily in all implementations. The various appearances of “an implementation,” “one implementation,” or “some implementations” in the preceding description are not necessarily all referring to the same implementations. Moreover, when terms or phrases such as “coupled” or “responsive” or “in response to” or “in communication with”, etc. are used herein or in the claims that follow, these terms should be interpreted broadly. For example, the phrase “coupled to” may refer to being communicatively, electrically and/or operatively coupled as appropriate for the context in which the phrase is used.

In the preceding description, various aspects of claimed subject matter have been described. For purposes of explanation, specific numbers, systems and/or configurations were set forth to provide a thorough understanding of claimed subject matter. However, it should be apparent to one skilled in the art and having the benefit of this disclosure that claimed subject matter may be practiced without the specific details. In other instances, well-known features were omitted and/or simplified so as not to obscure claimed subject matter. While certain features have been illustrated and/or described herein, many modifications, substitutions, changes and/or equivalents will now, or in the future, occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and/or changes as fall within the true spirit of claimed subject matter.

There is little distinction left between hardware and software implementations of aspects of systems; the use of hardware or software is generally (but not always, in that in certain contexts the choice between hardware and software may become significant) a design choice representing cost vs. efficiency tradeoffs. There are various vehicles by which processes and/or systems and/or other technologies described herein may be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle; if flexibility is paramount, the implementer may opt for a mainly software implementation; or, yet again alternatively, the implementer may opt for some combination of hardware, software, and/or firmware.

The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples may be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, may be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.).

Those skilled in the art will recognize that it is common within the art to describe devices and/or processes in the fashion set forth herein, and thereafter use engineering practices to integrate such described devices and/or processes into data processing systems. That is, at least a portion of the devices and/or processes described herein may be integrated into a data processing system via a reasonable amount of experimentation. Those having skill in the art will recognize that a typical data processing system generally includes one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and/or control systems including feedback loops and control motors (e.g., feedback for sensing position and/or velocity; control motors for moving and/or adjusting components and/or quantities). A typical data processing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems.

The herein described subject matter sometimes illustrates different components contained within, or coupled with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated may also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being “operably couplable”, to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art may translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B. 

The invention claimed is:
 1. A method to schedule requests for data from a memory, the method comprising: receiving, by a processor, a first thread from an application program being executed on an operating system, wherein the first thread includes at least a first request for data in the memory; receiving, by the processor, a second thread from the application program, wherein the second thread includes at least a second request for data in the memory; receiving, by the processor from the application program, a selection of a particular scheduling algorithm from among two or more scheduling algorithms to provide the selection of the particular scheduling algorithm to a scheduler in a memory controller, wherein the two or more scheduling algorithms include two or more of first-ready first-come-first-serve, network fair queuing, start-time fair queuing, stall-time fair memory scheduler, parallelism-aware batch scheduling, and batch scheduling with segregation, the application program contains the two or more scheduling algorithms, the particular scheduling algorithm effective to define an order to execute the first and second requests; controlling, by the processor, the scheduler within the memory controller to schedule the first and second requests in the order defined by the particular scheduling algorithm received from the application program; and wherein the particular scheduling algorithm comprises instructions to: segregate the first thread and the second thread into a first thread type and a second thread type based on how well the first and second threads are designed for use with parallel memory, wherein a thread of the first thread type issues requests of a first thread request type, and a thread of the second thread type issues requests of a second thread request type; form a first batch comprising the requests of the first thread request type and excluding the requests of the second thread request type; form a second batch comprising the requests of the second thread request type and excluding the requests of the first thread request type.
 2. The method of claim 1, further comprising executing the first batch before executing the second batch.
 3. The method of claim 1, wherein the batch scheduling with segregation comprises a batch algorithm and a within-batch scheduling algorithm.
 4. The method of claim 1, wherein the two or more scheduling algorithms comprise two or more of parallelism-aware within batch scheduling, total-max within batch scheduling, random within-batch scheduling, round-robin within-batch scheduling, and first-ready first-come-first-serve within-batch scheduling.
 5. A non-transitory computer-readable storage medium having computer-executable instructions stored thereon which, in response to execution by a computer, adapt the computer to perform a method to schedule requests for data from a memory, the method comprising: determining, by a processor, that a first thread from an application program being executed on an operating system has been received, wherein the first thread includes at least a first request for data in the memory; determining, by the processor, that a second thread from the application program has been received, wherein the second thread includes at least a second request for data in the memory; determining, by the processor, that a selection of a particular scheduling algorithm from among two or more scheduling algorithms has been received from the application program to provide the selection of the particular scheduling algorithm to a scheduler in a memory controller, wherein the two or more scheduling algorithms include two or more of first-ready first-come-first-serve, network fair queuing, start-time fair queuing, stall-time fair memory scheduler, parallelism-aware batch scheduling, and batch scheduling with segregation, the application program contains the two or more scheduling algorithms, the particular scheduling algorithm effective to define an order to execute the first and second requests; controlling, by the processor, the scheduler within the memory controller to schedule the first and second requests in the order defined by the particular scheduling algorithm received from the application program; and wherein the particular scheduling algorithm comprises instructions to: segregate the first thread and the second thread into a first thread type and a second thread type based on how well the first and second threads are designed for use with parallel memory, wherein a thread of the first thread type issues requests of a first thread request type, and a thread of the second thread type issues requests of a second thread request type; form a first batch comprising the requests of the first thread request type and excluding the requests of the second thread request type; form a second batch comprising the requests of the second thread request type and excluding the requests of the first thread request type.
 6. The computer-readable storage medium of claim 5, wherein the computer-executable instructions further include computer-executable instructions which, in response to execution by the computer, adapt the computer to perform the method that further comprises executing the first batch before executing the second batch.
 7. A computer system, comprising: a processor configured to control a scheduler within a memory controller of a memory; wherein the processor is configured to: receive a first thread from an application program being executed on an operating system, wherein the first thread includes at least a first request for data in the memory; receive a second thread from the application program, wherein the second thread includes at least a second request for data in the memory; receive from the application program, a selection of a particular scheduling algorithm from among two or more scheduling algorithms to provide the selection of the particular scheduling algorithm to a scheduler in a memory controller, wherein the two or more scheduling algorithms include two or more of first-ready first-come-first-serve, network fair queuing, start-time fair queuing, stall-time fair memory scheduler, parallelism-aware batch scheduling, and batch scheduling with segregation, the application program contains the two or more scheduling algorithms, the particular scheduling algorithm effective to define an order to execute the first and second requests; control the scheduler within the memory controller to schedule the first and second requests in the order defined by the particular scheduling algorithm received from the application program; and wherein the particular scheduling algorithm comprises instructions to: segregate the first thread and the second thread into a first thread type and a second thread type based on how well the first and second threads are designed for use with parallel memory, wherein a thread of the first thread type issues requests of a first thread request type, and a thread of the second thread type issues requests of a second thread request type; form a first batch comprising the requests of the first thread request type and excluding the requests of the second thread request type; form a second batch comprising the requests of the second thread request type and excluding the requests of the first thread request type.
 8. The computer system of claim 7, wherein the processor is further configured to control the memory controller to execute the first batch before execution of the second batch.
 9. The computer system of claim 7, wherein the batch scheduling with segregation comprises a batch algorithm and a within-batch scheduling algorithm.
 10. The computer system of claim 7, wherein the two or more scheduling algorithms comprise two or more of parallelism-aware within batch scheduling, total-max within batch scheduling, random within-batch scheduling, round-robin within-batch scheduling, and first-ready first-come-first-serve within-batch scheduling.
 11. The computer system of claim 7, further comprising the memory and the memory controller, which is coupled to the processor and to the memory. 